Chronic obstructive pulmonary disease (COPD) is a major public health problem and is the fourth leading cause of death in the United States. Despite pharmacologic and surgical therapy, COPD continues to cause considerable morbidity, and patients suffer from exercise intolerance and decreased physical activity, which are independent risk factors for exacerbations, hospitalizations, and mortality.Pulmonary rehabilitation (PR) has been shown to improve symptoms of dyspnea, health-related quality of life, and exercise capacity and national guidelines now recommend that all patients with COPD participate in such programs. Unfortunately, long-term exercise adherence after initial rehabilitation is very poor, and it is clear that benefits gained during PR diminish rapidly if patients do not continue to exercise. There remains a critical need for novel interventions that may sustain the benefits of regular exercise after PR, as well as promote long-term exercise adherence and exercise self-efficacy in the post-rehabilitation period in patients with COPD. Tai chi is a popular mind-body exercise that incorporates low-moderate intensity physical activity, self awareness, relaxation, and meditative slow breathing. It may be particularly suited to deconditioned individuals with COPD who suffer from limited exercise tolerance and dyspnea. Importantly, tai chi exercise comprehensively integrates several key elements of PR (aerobic exercise, upper and lower extremity training, breathing, and stress management) into one relatively low-cost and accessible activity. Studies in varied populations have suggested that tai chi can improve exercise capacity, quality of life, and promote exercise self-efficacy; and that adherence may be favorable when compared to conventional exercise modalities. In this application, we propose a three-arm randomized controlled trial in patients with COPD (N=126) to evaluate the benefits of six months of tai chi exercise, versus group walking, versus general recommendations for self-exercise (standard care) in maintaining clinical improvements after the completion of standard, supervised PR. Our primary aim will be to investigate whether tai chi can maintain gains in exercise capacity three and six months after PR. Secondary aims will examine quality of life, dyspnea, mood, activites of daily living, as well as exercise self-efficacy, intervention adherence and overall activity. Long-term follow-up assessment will be conducted at 1 year. The results of the proposed project have the potential to transform the clinical care of patients with COPD by providing a new strategy that may substantially extend the benefits of PR and promote continued physical activity in this population.